Metallaheteroborane chemistry. Part 7. Synthesis, crystal structure, and characterisation of two dinuclear rhodatelluraboranes, [{(PPh3)2RhTeB10H10}2] and [(PPh3)(CO)Rh2Te2B20H20]

Abstract

The dinuclear rhodatelluraborane closo-[(PPh₃)(CO)Rh₂Te₂B₂₀H₂₀](2) was obtained from the reaction between either [Os₃H₂(CO)₁₀] and closo-[2,2-(PPh₃)-2-H-1,2-TeRhB₁₀H₁₀](1) in dichloromethane solvent, or [Rh(cod)(PPh₃)Cl](cod = cyclo-octa-1,5-diene) and Cs[TeB₁₀H₁₁] in ethanol. The reaction between [Mo(CO)₆] and closo-[2,2-(PPh₃)₂-2-H-1,2-TeRhB₁₀H₁₀] in tetrahydrofuran afforded [{closo-(PPh₃)RhTeB₁₀H₁₀}₂], (3). X-Ray crystallographic analysis of compound (2) shows it to crystallise with a monoclinic space group (P2₁/c), containing four molecules in a unit cell of dimensions a= 16.213(4), b= 13.082(4), c= 17.048(3)Å, and β= 95.29(2)°, The final R factor was 0.028 for 5 992 observed reflections. X-Ray analysis of the CH₂Cl₂ solvate of (3) shows the crystal to be monoclinic, space group P2₁/a with four molecules in a unit cell that measures a= 16.384(5), b= 16.197(6), c= 19.879(5)Å, and β= 70.84(2)°. The final R factor was 0.039 for 3 973 observed reflections. Both (2) and (3) contain two {RhTeB₁₀} cages bonded by Rh–Rh′, Rh–B′, Rh′–B, Rh–H′–B′, and Rh′–H–B′, interactions. Principal interatomic distances are Rh–Rh′ 2.737 1 (3), Rh–B′ 2.380(4), Rh′–B 2.329(4), Rh–Te 2.565 3(3), Rh′–Te′ 2.581 7(3)Å in (2) with the corresponding distances in (3), 2.834 4(12), 2.354(12), 2.341(13), 2.604 7(12), and 2.581 1 (10)Å respectively. The exo-cage ligands (PPh₃ or CO) in both (2) and (3) adopt cis configurations about the central Rh–Rh′ portions of the molecules. The ¹H, ¹¹B, and ³¹P n.m.r. data for (2) and (3) show close similarities with those of (1).